Glycogen metabolism is under the control of several hormones, including insulin and catecholamines, and covalent phosphorylation of certain key enzymes is thought to be involved in such regulation. Glycogen synthase in vitro is subject to a particularly intricate interconversion, undergoing phosphorylation at several distinct sites through the action of at least four different types of protein kinase: (1) cAMP-dependent protein kinases, (2) phosphorylation kinase, (3) PC 0.4/PC 0.5 and (4) PC 0.7. One emphasis of the proposal is the continued characterization of this interconversion in vitro seeking to relate the action of a given kinase with phosphorylation of specific sites. In addition, the further purification and characterization of the PC 0.4/PC 0.5 and PC 0.7 protein kinases will be undertaken. A second emphasis will be an attempt to evaluate how far the conversion studied in vitro is functional in intact muscle. One important question is of the role of Ca2 ion in regulating glycogen synthase activity. Insofaras hormone action is mediated by the action of protein kinases, knowledge of the specificities of the different kinases in vitro should identify which kinase(s) is a candidate to mediate different hormonal and other treatments.